The subject matter disclosed herein relates to a heat pump and in particular to a heat pump valve arrangement that prevents migration of liquid refrigerant.
A heat pump is a device used in heating, ventilating and air conditioning (HVAC) applications. Heat pumps are desirable because the same components may be used to provide both heating and cooling operations. Typically, during cooling operations, a heat pump will include an outdoor unit having a heat exchanger (condenser) coupled to a compressor that circulates liquid refrigerant to a heat exchanger (evaporator) having an expansion valve located in an indoor unit. The evaporator absorbs heat from the area or structure and circulates gaseous refrigerant back to the condenser where heat is dissipated into the environment. This thermodynamic cycle is referred to as a vapor-compression refrigeration cycle. The heat pump also includes a reversing valve that allows the flow of refrigerant to be reversed, such that when heating operation is desired, the refrigerant absorbs heat from the environment with the outdoor unit heat exchanger and transfers the heat to the indoor unit.
In most refrigeration cycles, there is a tendency for liquid refrigerant to try to migrate through the liquid line between the indoor heat exchanger and the outdoor heat exchanger. When this occurs, some of the liquid refrigerant migrates into the compressor, settling in the oil sump located in the bottom of the compressor. When the compressor is next operated, the liquid refrigerant boils into a gaseous state and exits the compressor. Unfortunately, when this occurs the refrigerant carries a portion of the compressor oil, reducing the amount of lubricant in the compressor. It should be appreciated that the loss of lubricant may cause increased wear and be detrimental to the reliability and life of the compressor.
The refrigerant carries the compressor oil through the refrigeration system. With each cycle of the refrigerant, a portion of the oil is deposited back into the compressor. While in small refrigeration systems the removal of oil from the compressor is tolerated since a smaller system will also cycle the refrigerant through the system faster allowing the oil to return to the compressor. However, in larger systems that have larger volumes of refrigerant and longer cycles, the loss of oil from the compressor may be a cause for concern.
Heat pumps are installed and operated in many environments and applications. Due to technical, or aesthetic reasons, the outdoor and indoor units may be located some distance and elevation apart. It should be appreciated that as the length of the line set between the outdoor and indoor units increases, the volume of refrigerant in the heat pump needs to be increased. As a result, when the line set increases beyond a threshold distance, additional components need to be added to avoid migration of liquid refrigerant into the compressor. Typically, this is accomplished by adding a normally closed solenoid valve to the input line to the outdoor heat exchanger. The solenoid valve is powered by a relay that is coupled to the control for the compressor. While the solenoid valve is suitable for preventing migration of the liquid refrigerant, it is undesirable since it requires an additional step to the installation process and also uses additional electrical power reducing the efficiency of the heat pump. Further, the energy requirements of the solenoid valve may require the installer to change other components within the heat pump such as a transformer.